Electrolytic process for producing tetraalkyl lead compounds



K. C. SMELTZ July 9, 1968 Filed June 23, 1964 CATHOLYTE CATHOLYTE E T um b A 2 w 0 a a m Q. 5 m l m i ,& W. v Ill I I! l// f A N R 4 k m a: m am l O N A INVENTOR KENNETH C. SMELTZ ATTORNEY United States Patent3,392,093 ELECTROLYTIC PROCESS FOR PRODUCING TETRAALKYL LEAD COMPOUNDSKenneth C. Smeltz, Wilmington, Del., assignor to E. I.

du Pont de Nemonrs and Company, Wilmington, Del.,

a corporation of Delaware Filed June 23, 1964, Ser. No. 377,312 17Claims. (Cl. 20472) This invention relates to a process for producingtetraalkyl lead compounds and particularly to an improved process forpreparing those compounds by the electrolytic reduction of an alkylhalide at a lead cathode.

Electrolytic syntheses of organometals are known. For example, Tafel,Ber., 44, 327 (1911), obtained tetraisopropyl lead by electrolyzing anaqueous acid solution of acetone at a lead cathode in the absence ofair. Such method, however, is not general and appears impractical fororganolead production because of low yields and side reactions. Later(in 1925) Calingaert and Mead disclosed tetraalkyl lead formation at alead cathode by electrolyzing a catholyte consisting of an alkyl halidein either alcoholic caustic (Calingaert in US. Patent 1,539,- 297) oraqueous caustic containing casein (Mead in US. Patent 1,567,159). Theyhypothesized: Apparently the hydrogen formed at the cathode reduces thereaction mass, forming lead di-ethyl, which is unstable at thetemperature of the catholyte, and breaks up thermally into lead and leadtetraethyl. The above disclosure suggests that a potential source ofhydrogen is necessary, such as the hydroxylic solvent employed, andfurther that, if diethyl lead is an intermediate, the yield based onlead can be no more than 50% of the consumed lead. In fact, under thedisclosed conditions the tetraethyl lead yields tend to be loW and thecathode deteriorates. Further, the ethylating agent tends readily to bedestroyed in side reactions, by reaction for example with the causticpresent, particularly in alcohol.

Besides the cathodic processes, anodic oxidations have also beenemployed to produce organometallics, as for example by Hein et al., Z.anorg. Allgem. Chem. 141, 161 (1924), who obtained tetraethyl lead byelectrolyzing sodium zinc triethyl at a lead anode, and by Ziegler inBritish Patent 814,609 (1959) who discloses synthesis of Group IIV metalalkyls 'by electrolyzing a complex aluminum alkyl at an anode composedof the Group II-V metal. Numerous other references disclose similarprocesses. All such anodic processes are characterized by the fact thatthe source of the organic groups to begin with is invariably anotherorganometal (often a complex of two Or more such compounds), the netresult of the electrolytic oxidation being replacement of metal in thestarting material by metal of the anode. That the anodic processrequires organometal starting material is an important disadvantage, forsuch materials normally are difiicult or costly to make and requirespecial storage and handling under inert atmospheres.

Ernest F. Silversmith and Walter J. Sloan, in their copendingapplication, Ser. No. 156,128, filed Nov. 30, 1961, and now Patent No.3,197,392, have disclosed a novel process for preparing organometalcompounds, including tetraalkyl lead compounds, by electrolyzing, at acathode of the selected metal, a solution of an alkylating agent in anormally liquid, non-hydroxylic catholyte. They disclose that it is notnecessary to maintain rigorous anhydrous conditions in the catholyte andthat traces of water therein can be tolerated. They also disclose thatthey can employ, as the anolyte, an aqueous solution of sodiumcarbonate. It is probable that, when such anolyte is used with theion-permeable membrane employed by Silversmith and Sloan, water willgradually pass through the membrane into the catholyte so the catholyte,which 3,392,093 Patented July 9, 1968 initially is non-hydroxylic, willeventually contain considerable uncontrolled amounts of water.

The process of Silversmith and Sloan is very efiective and constitutes asignificant advance in the art. However, improvements in that processare desirable; Current densities must be kept relatively low foreflicient current utilization. Attempts to achieve high cell productionrates by operating at high current densities are stymied by thedecreasing ability of the process to make tetraalkyl lead etficiently ascurrent density is increased above certain limits. In other words, abovesuch limiting current densities, the electrode reaction becomes less andless specific for the formation of tetraalkyl lead While gas-formingside reactions (at the expense of current and alkylating agent) becomeincreasingly prominent. The process also tends to be erratic anddifiicult to control over long periods of operation. The voltagerequired for maintaining current density at the selected operating leveltends to increase with time while the highest current density that maybe used for smooth operation (high tetraalkyl lead electrical yield withminimum side reactions) tends to decrease. The overall results are stillhigher electrical costs and lower production rates. Furthermore, therecovery of by-product bromine from the anolyte is more complicated,difiicult and costly than is desired.

It is an object of this invention to provide a new and improvedelectrolytic process for producing tetraalkyl lead compounds. Anotherobject is to provide such a process which overcomes objections of theprior electrolytic processes and which produces higher yields oftetraalkyl lead compounds at higher production rates and in a moreeconomical manner. A further object is to provide such a process whichinvolves conditions that increase the specificity of the reaction toproduce tetraalkyl lead compounds at the expense of side reactions andpermits the use of higher current densities. A particular object is toprovide such a process which can be operated in a continuous manner. Astill further object is to provide such a continuous process which canbe operated over long periods of time at high current densities and lowvoltages without loss of efficiency and decrease in yield and productionrates. Other objects are to advance the art. Still other objects andadvantages will be apparent from the detailed description presentedhereinafter.

The foregoing and other objects may be accomplished in accord with thisinvention which comprises an electrolytic process for producingtetraalkyl lead compounds at a lead cathode in an electrolytic cellhaving a lead cathode, an anode of a material which is resistant toattack by halogens of atomic numbers 17 to 53, and a currentpermeablepartition separating the catholyte from the anolyte, which processcomprises:

(A) passing an electrolyzing direct electric current through (B) aliquid catholyte which initially consists essentially (a) an alkylhalide in which the alkyl group has 1-10 carbon atoms and the halogenatom has an atomic number of at least 17,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1-18 carbonatoms and the halogen atom has an atomic number of at least 17, saidcurrent-carrier being in a concentration sufiicient to provide acatholyte having a conductivity of at least 0.001 ohm cm. and

(c) from about 1 to 20 moles per mole of said current-carrier of atleast one hydroxylic compound of the class consisting of water andalkanols of l-4 carbon atoms; and

(C) a liquid anolyte which initially consists essentially of a solutionof (1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1-18 carbonatoms and the halogen atom has an atomic number of at least 17, in aconcentration sufiicient to provide an anolyte having a conductivity ofta least 0.001 ohrn cm.-

(2) in an inert solvent having a reduction potential at least as high assaid alkyl halide and an oxidation potential higher than saidcurrent-carrier;

(D) during the electrolysis, adjusting the amounts of thecurrent-carrier in the catholyte and the anolyte as may be necessary tomaintain their conductivities at at least 0.001 ohm cm. and adjustingthe amount of the hydroxylic compound in the catholyte as may benecessary to maintain the concentration thereof within the range of fromabout 1 to about moles per mole of current-carrier; and

(E) recovering tetraalkyl lead from the catholyte.

While the process may be operated without a solvent in the catholyte, itusually will be preferred to employ an inert nonhydroxylic organicsolvent for both the alkyl halide and the current-carrier, which solventhas a reduction potential higher than the alkyl halide and an oxidationpotential higher than the current-carrier. By an inert" solvent is meanta solvent or mixture of solvents which is nonreactive to the othercomponents of the catholyte and the anolyte and the reaction productsproduced therein, i.e. nonreactive to the tetraalkyl lead, the alkylhalide, the hydroxylic compound, the tetraalkyl ammonium monohalides andpolyhalides, and halogens of atomic numbers of at least 17. Thus, thereare excluded strong acids (reactive to tetraalkyl lead), strong bases(reactive to alkyl halide and halogen), and organometallic compoundssuch as diethyl zinc, triethyl aluminum and diethyl magnesium (reactivetowards hydroxylic compound and tetraalkyl ammonium polyhalides), andthe like.

The hydroxylic compound in the catholyte consists of water or an alkanolof 1-4 carbon atoms, i.e. methanol, ethanol, l-propanol, 2-propanol,l-butanol, 2-butanol, 2- methyl-l-propanol, 2-methy1-2-propanol, andmixtures of any two or more thereof. Water, methanol and ethanol,particularly water, are preferred. The hydroxylic compound will beemployed in a proportion of from about 1 to 20 moles per mole oftetraalkyl ammonium monohalide, preferably from about 3 to about 10moles per mole.

It has been found that, by the use of catholytes and anolytes of theforegoing defined compositions, the dilficulties encountered with theprior processes are largely overcome and many significant advantages areobtained. Particularly, the use of the controlled amounts of thehydroxylic compounds in the catholyte in the proportions and in themanner required by this invention materially improves the specificity ofthe tetraalkylation reaction, that is, it suppresses side reactions andcauses more of the alkyl halide to react with the lead of the cathode toform tetraalkyl lead instead of other products, whereby the yields oftetraalkyl lead are increased, whether based on current or on cathodiclead consumed. Other things being equal, the production rate, i.e. thetotal amount of tetraalkyl lead produced at a given cathode in a giventime, theoretically should increase with increase in the currentdensity. However, as pointed out hereinbefore, increase in the currentdensities in the prior processes results in lower yields of tetraalkyllead and large increases in side reactions and the production of gaseousby-products and loss of current efiiciency. The hydroxylic compounds inthe catholyte in the amounts employed in this invention make it possibleto use current densities considerably higher than can be usedpractically in the prior processes, by suppressing the side reactionsthat normally occur at such higher current densities, thereby making itpossible to obtain production rates which cannot be obtained by theprior processes. Also, the use of the hydroxylic compounds in thecatholyte according to this invention makes it possible, by judiciousregulation of the concentration of the hydroxylic compound, to obtain adesired high current density and to maintain it throughout theelectrolysis with the use of lower and more uniform cell voltages thancould be used heretofore, particularly with cell partitions ofsubstances which exhibit inherently high resistance in low hydroxylic ornon-hydroxylic electrolyte systems, whereby reaction control is madeeasier and electrical costs lower. In other words, by regulation of theconcentration of the hydroxylic compound in the catholyte, it ispossible to maintain a highly efiicient production of tetraalkyl leadcompound in high yields and at high produc tion rates throughout theelectrolysis and particularly over long periods of continuous operationwith minimum cell voltage requirements. These results are not obtainableby the use of the aqueous caustic, alcoholic caustic or the like aqueoussolutions employed in the catholytes and/or anolytes of the priorprocesses and which are excluded by the present invention.

It appears that the hydroxylic compound, as employed in this invention,exerts its beneficial influences on the electrode reaction itself, byfunctioning within the electrical double layer around the cathode or atthe cathode surface itself (in an unobvious manner in view of the priorart), to favor the conversion of alkyl halide and cathodic lead totetraalkyl lead over their conversion to gaseous products andsludge-containing lead.

'Such beneficial eflects of the hydroxylic compound are not, as mighthave at first been expected, attributable to increased conductivity ofthe otherwise non-hydroxylic catholyte composition. Except at relativelyhigh tetraalkyl ammonium monohalide (salt) concentrations (e.g. aboveabout 0.5 mole/kg. of solution) where slight to moderate conductivityincreases can be observed, addition of water, in the amounts hereinvolved, has little or no effect on solution conductivity. Increase insolution conductivity, when observed at the higher salt concentrations,apparently derives from the etfect of water to decrease solutionviscosity at those salt concentrationss. Decrease in the overall cellvoltage requirement, when observed, apparently results from theunobvious effect of the hydroxylic compound to increase current flowacross the cell partition, possibly by facilitating ion transport fromone compartment to the other, irrespective of its elfect on theconductivity of the catholyte solution itself.

The concentration range of l to 20 moles of hydroxylic compound per moleof tetraalkyl ammonium monohalide appears to be critical. Below thespecified lower limit of 1 mole, the beneficial elfects are not alwaysattained to the desired degree and gassing occurs when the currentdensity is increased to 0.1 amp/sq. cm., while above the range, gassingtends to be excessive and the tetraalkylation ineflicient. Within thebroad range, the concentration of hydroxylic compound will varydepending primarily on the alkyl halide and the tetraalkyl ammoniummonohalide, particularly on the nature of the halogens, and on theeffect desired. Bromides and iodides respond better to the presence ofthe hydroxylic compound for the purposes of the invention, and, ingeneral, the higher proportions of hydroxylic compound are used withthese halides.

The hydroxylic compound, e.g. water, may be introduced into the cathodecompartment directly, in an intermittent or a continuous manner, as suchor in combination with any of the other catholyte ingredients, or it maybe introduced in part from the anode compartment during the course ofthe electrolysis by employing an aqueous anolyte solution and a cellpartition which permits water transport into the cathode compartment.

This invention is concerned primarily with the manufacture of tetraalkyllead antiknock compounds such as tetramethyl lead, tetraethyl lead, andtetra(mixed methyl and ethyl) lead compounds, but the process isapplicable to the preparation of other tetraalkyl lead compounds havingup to carbon atoms in each alkyl group. Thus, the alkylating agent willbe an alkyl halide in which the alkyl group has 1-10 carbon atoms andthe halogen has an atomic number of at least 17, i.e. chlorine, bromineor iodine, or a mixture of any two or more of such alkyl halides. Suchalkyl halides have reduction potentials of 1-2 volts (at a lead cathoderelative to a saturated calomel electrode and determined in a solutionof tetraethyl ammonium monobromide in acetonitrile at 20 C. to 80 C.).Preferably, the alkyl halides will have 1-2 carbon atoms, i.e. will bemethyl halides, ethyl halides or a mixture of a methyl halide and anethyl halide, and most preferably the bromide or bromides.

When a solvent (and diluent) for the alkyl halide is employed in thecatholyte, it usually and preferably will be an alkanonitrile in whichthe alkyl group has 1-5 carbon atoms, it being understood that the termalkanonitrile means compounds of the formula RCN wherein R represents analkyl radical. Representative alkanonitriles are acetonitrile,propionitrile, n-butyronitrile, isobutyronitrile, n-amylnitrile,isoamylnitrile, and pivalonitrile. Mixtures of any two or more of suchalkanonitriles may be used. Acetonitrile is usually preferred. Otherinert nonhydroxylic organic solvents, which have higher reductionpotentials than the alkyl halides and higher oxidation potential thanthe tetraalkyl ammonium halides and which are solvents for both thealkyl halide and the tetraalkyl ammonium monohalide, can be employed inplace of the alkanonitrile or in admixture therewith. Suitable solventsinclude carboxamides such as N,N-dimethylformamide andN,N-dimethylaceta.mide. The higher reduction potential is required tocause preferential reduction of the alkyl halide at the cathode. Thehigher oxidation potential is required to cause preferential oxidationof the tetraalkyl ammonium monohalide at the anode.

The current-carrier, which is employed in the catholyte and in theanolyte, must consist of at least one (one or more) current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan the alkyl halide and in which each alkyl group has 1-18 carbonatoms and the halogen has an atomic number of at least 17. Suchcurrent-carrying tetraalkyl ammonium monohalides can be represented bythe formula R NX wherein each R is an alkyl radical of from 1-18 carbonatoms and X is a halogen atom which has an atomic number of at least 17,i.e. chlorine, bromine and iodine. The alkyl radicals in a tetraalkylammonium monohalide may be the same or different. Mixtures of two ormore tetraalkyl ammonium monohalides may be used. Also, the tetraalkylammonium monohalide must have a higher reduction potential than thealkyl halide employed, so as not to interfere with the alkylhalide-electrode reaction.

Representative tetraalkyl ammonium monohalides are:

Tetramethylammonium bromide Tetramethylammonium iodideTetraethylammonium chloride Tetraethylammonium bromideTetraethylammonium iodide Tetra(n-propyl)ammonium bromideTetra(n-butyl)ammonium chloride Tetra(n-butyl)ammonium bromideTetra(n-butyl)ammonium iodide Tetra(n-amyl)ammonium bromide Tetra(n-amyl ammonium iodide Trimethylethylammonium bromideTrimethylisoamylammonium bromide Dimethyldiethylammonium bromideMethyltriethylammonium bromide Dioctadecyldimethylammonium chlorideOctadecyltrimethylammonium bromide The current-carrying tetraalkylammonium monohalides are employed in the catholyte and in the anolyte inconcentrations suflicient to provide electrical conductivities in eachof at least 0.001 ohm" cmr preferably at least about 0.01 ohmcmr and ashigh as is practicable. Thus, the tetraalkyl ammonium monohalide must besoluble in the other components of the catholyte and the anolyte,respectively, to the extent required to produce those concentrations.The maximum obtainable conductivity is determined by such factors as theparticular tetraalkyl ammonium monohalide, the solvent and itsdielectric constant and viscosity, and the other components of theelectrolyte compositions and their character. The actual amount oftetraalkyl ammonium monohalide required to achieve a particularconductivity level (0.001 and higher) will vary with the varioustetraalkyl ammonium monohalides, the various solvents, the varioushydroxylic compounds, the relative concentrations of the differentmaterials, and the temperature of operation. In view of these variables,it is impossible to specify absolute ranges for all possible catholytesand anolytes within the scope of this invention. However, it is wellknown to the art to impart electrical conductivity to normallynonconductive organic liquids, including nonhydroxylic organic liquds,by means of current-carryng solutes, and hence those skilled in the arthave the knowledge to readily determine the proportions required for anyparticular electrolyte materials. This practice and the materialsemployed are disclosed by S. Swann, Jr., in the chapter beginning onpage 385 of Technique of Organic Chemistry, A. Weissberger, editor, vol.II, 2nd ed. (1956), Interscience, N.Y., N.Y., and in the followingliterature:

(a) Harned and Owen, The Physical Chemistry of Electrolytic Solutions,3rd ed., Reinhold, N.Y. (1950).

(b) Fuoss and Accascina, Electrolytic Conductance,

Interscience, N.Y. (1959).

(c) Tables Annuelles de Constantes et Donnies Numeriques 18,Conductivity of Electrolytes, Hermann, Paris (1937).

(d) Audrieth and Kleinberg, Non-Aqueous Solvents (Applications as Mediafor Chemical Reactions), John Wiley and Sons, N.Y. (1953).

The following illustrate the conductivities of some representativeelectrolyte compositions and variations thereof with variations in thematerials, concentrations and temperatures. The conductivity of a 10%wt. solution of tetraethyl ammonium monobromide in acetonitrile is 0.027ohm cm.- at 50 C. An electrolyte which consists of 10% wt. tetraethylammonium monobromide, 3% wt. water, and the rest acetonitrile,corresponding to 0.05 gm. rnole Et NBr/kg. of electrolyte, has aconductivity of 0.028 ohmcm. at 25 C. A 33% wt. tetrabutyl ammoniummonobromide in 67% wt. of methyl bromide, corresponding to about 1.1 gm.mole Bu NBr/kg. total compositions, has a conductivity of 0.0011 ohmcm.-at 9 C.11 C. A 12% wt. Bu NBr/88% MeBr solution has a conductivity of0.0015 ohm cm.- at 9 C.-11 C. The conductivities of compositionscontaining various amounts of tetraethyl ammonium monobromide (Et NBr)in a solution of 4% wt. water, 15% wt. MeBr and 5% wt. tetramethyl leadin acetonitrile to make at 25 C.

is shown in the following Table A:

TABLE A EtiNBr, Cone.

Conductivity, ohm- Percent wt. Gm.-Moleslkg. cm.-

These data shown that a conductivity of about 0.001 ohm cm.- can beachieved with as little as 0.01 gm. mole of tetraethyl ammoniummonobromide per kilogram of catholyte; and that a conductivity of atleast about 0.01 ohm" cm. can be obtained with at least about 2% byweight of tetraethyl ammonium monobromide, i.e. about 0.1 gm. mole EtNBr/kg. catholyte.

Generally, the concentration of the current-carrying tetraalkyl ammoniummonohalide in the catholyte will be in the range of about 0.01 to about3 gram moles per kilogram of catholyte, more usually from about 0.1 toabout 2 gram moles per kilogram. When the catholyte does not include asolvent and diluent for the alkyl halide, the tetraalkyl ammoniummonohalide usually will be in a concentration of from about 0.005 toabout 0.5 mole, preferably from about 0.025 to about 0.25 mole, per moleof the alkyl halide, particularly when the alkyl groups in the alkylhalide have l2 carbon atoms and the alkyl groups in the tetraalkylammonium monohalides have l4 carbon atoms. Typical catholytecompositions which do not include a solvent are (I) 1 part by weight ofmethyl bromide, 0.5 part of tetrabutyl ammonium monobromide and 0.25part of methanol (corresponding to a molar ratio of 5/1), and (II) 1part by weight of methyl bromide, 0.27 part of tetrabutyl ammoniummonobromide and 0.07 part of water.

As pointed out heretofore, the catholyte may, and usually will contain,an inert nonhydroxylic organic solvent for both the alkyl halide and thecurrent-carrying tetraalkyl ammonium monohalide, which solvent has areduction potential higher than the alkyl halide and an oxidationpotential higher than the tetraalkyl ammonium monohalide. Such solventmay be present in any desired amount to act as a diluent for the alkylhalide, but usually will be in an amount sufiicient to dissolve all ofthe alkyl halide, e.g. sufficient to constitute from about 39% to about97% by weight of the catholyte composition. Preferably, when analkanonitrile is employed as the solvent, and particularly when thealkyl halides have 1-2 carbon atoms and the alkyl groups of thetetra-alkyl ammonium monohalides have 1-4 carbon atoms, the catholyteinitially will consist essentially of (a) from about 0.1 to about 3 grammoles, most preferably from about 1 to about 2 gram moles, of alkylhalide per kilogram of catholyte; (b) from about 0.1 to about 1 grammole, most preferably from about 0.25 to about 0.5 gram mole, ofcurrent-carrying tetraalkyl ammonium monohalide per kilogram ofcatholyte; and (c) from about 1 to 20 moles, most preferably from about3 to about moles, of hydroxylic compound per mole of current-carryingtetraalkyl ammonium monohalide; (d) the rest of the catholyte consistingessentially of the alkanonitrile.

The alkyl halide, the tetraalkyl ammonium monohalide, the hydroxyliccompound and, when present, the solvent are readily coordinated in thecatholyte to provide a suitably conductive reaction medium for theformation of tetraalkyl lead. When an alkyl chloride is employed as thealkylating agent, the tetraalkyl ammonium monohalide preferably will bea bromide or an iodide. However, an all bromide system is preferred,that is, one in which an alkyl bromide is employed in the catholyte anda tetraalkyl ammonium monobromide is employed in both the catholyte andthe anolyte.

The catholyte may also contain substances which are thermal stabilizersfor tetraalkyl lead compounds and which are otherwise inert in theelectrolytic process. A wide variety of stabilizers are known (e.g.Calingaert in US. Patents 2,660,591-6, and others). iMore specifically,there may be used one or more hydrocarbons, in-

cluding saturated, unsaturated and aromatic hydrocarbons, boiling in therange of 70 C. to 250 C. at atmospheric pressure, e.g., isooctane,diisobutylene, terpenes, toluene, xylene, naphthalene andalpha-methylnaphthalene. In accordance with art-recognized principles,the stabilizer is normally chosen with due regard for the volatility ofthe tetraalkyl lead compound to be stabilized and usually amounts tofrom about 0.1% to about 30% by weight of such compound.

The anolyte, that is employed in the process of this invention,initially consists essentially of -a solution of (l) a current-carrierwhich consists of at least one ourrent-carrying tetraalkyl ammoniummonohalide which has a higher reduction potential than the alkyl halideemployed and in which each alkyl group has 1-18 carbon atoms and thehalogen atom has an atomic number of at least 17, in a concentrationsufficient to provide an anolyte having a conductivity of at least 0.001ohrn cmf (2) in an inert solvent having a reduction potential at leastas high as the alkyl halide and an oxidation potential higher than thecurrent-carrying tetraalkyl ammonium monohalide. The suitable tetraalkylammonium monohalides and the amounts thereof required to produce aparticular desired conductivity have been disclosed and discussedhereinbefore in connection with the catholyte. The solvents, which havebeen disclosed to be suitable for use in the catholyte, are alsosuitable for use in the anolyte. Also, the compositions, that have beendisclosed hereinbefore to be suitable as catholytes, are suitable foruse as the anolytes, and the composition of the anolyte initially may bethe same as that of the catholyte. The solvent in the anolyte may be analkyl halide of the class that is suitable for use as the alkylatingagent, in which case, the solvent will have a reduction potential equalto that of the alkyl halide in the catholyte. When solvents, other thanthe alkyl halide, are used in the anolyte, they should have a reductionpotential higher than the alkly halide in the catholyte. In addition,the solvent in the anolyte need not be a nonhydroxylic organic solvent(as required in the catholyte) provided that it has the other specifiedcharacteristics. Water and alkanols of 1-4 carbon atoms are particularlysuitable as solvents in the anolyte. Usually, the solvent in the anolytewill consist of at least one solvent of the group consisting of water,an alkanol of 14 carbon atoms, and an alkanonitrile in which the alkylgroup has l5 carbon atoms. The tetraalkyl ammonium monohalide, employedin the anolyte, may be the same as or dilferent from that employed inthe catholyte, but usually will be the same. Preferably, it will be abromide, particularly when the alkyl halide is a bromide. Preferably,the solvent in the anolyte consists of water, particularly when thehalogen of the alkyl halide and of the tetraalkyl ammonium monohalide isbromine. Also, preferably, the alkyl groups in the tetraalkyl ammoniummonohalide in the anolyte will have l2 carbon atoms, e.g. tetraethylammonium monobromide or tetramethyl ammonium monobromide.

The concentration of the current-carrying tetraalkyl ammonium monohalidein the anolyte will be sufiicient to provide the desired conductivityand will vary widely depending upon the particular tetraalkyl ammoniummonohalide, the particular solvent, and the temperature employed,according to the principles hereinbefore discussed. In general, thecurrent-carrying tetraalkyl ammonium monohalide may be in aconcentration as low as 2% by weight up to about 50% by weight,particularly when a lower tetraalkyl ammonium monohalide is employedwith a lower alkanol such as methanol and ethanol, as the solvent.Usually, the concentration of the current-carrying tetraalkyl ammoniummonohalide will be in the range of from about 2% to about 30% by weight,preferably from about 5% to about 10%, and most usually about 5%,particularly when the alkyl groups of the tetraalkyl ammonium monohalidehave l4 carbon atoms and the solvent is water, an alkanol of 1-2 carbonatoms, an alkyl halide of 12 carbon atoms, or acetonitrile.

In the electrolysis, halide ion is produced at the cathode; at the sametime at the other side of the membrane halide ion is oxidized at theanode to halogen. Such halogen reacts with the current-carryingtetraalkyl ammonium monohalide of the anolyte to form a complextetraalkyl ammonium polyhalide which, in the presence of excesstetraalkyl ammonium monohalide, normally is the trihalide, R NX and insome cases may be the tetrahalide, R NX or even the pentahalide, R NXSuch tetraalkyl ammonium polyhalides normally are solids and are fairlyinsoluble in water, but are more soluble in alkanols and alkanonitriles.The tetraalkyl ammonium polyhalides can be recovered from the anolytesolutions, most readily from the solutions of current-carryingtetraalkyl ammonium monohalide in water, and then treated by knownmethods to readily release the excess halogen as elemental halogen andto regenerate the current-carrying tetraalkyl ammonium monohalide. Whenthe halide compounds employed are bromides, the alkyl groups of thecurrent-carrying tetraalkyl ammonium monobromides contain l2 carbonatoms and the anolyte SOlVent is water, the tetraalkyl ammoniumpolybromides formed in the anolyte include the tribromides, thetetrabromides and the pentabromides, all of which are normally solidswhich are insoluble in the anolyte solution and separate therefrom. Ifthe anolyte is maintained at a temperature of about 45 C. or above, suchmixture of tetraalkyl (methyl and ethyl) ammonium polybromides separatesfrom the anolyte solution as a Water-immiscible, heavy liquid phasewhich can be most readily removed from the anode compartment.

The process of this invention is conducted in an elec trolytic cellwhich has a lead cathode, an anode of a material which is resistant toattack by halogens of atomic numbers 17 to 53, and a current-permeablepartition which separates the cell into a cathode compartment and ananode compartment, thereby separating the catholyte from the anolyte.Usually, the effective surfaces of the electrodes will be spaced apartby about 0.5 to about 2 cm. The catholyte and the anolyte are placed intheir respective compartments and an electrolyzing direct electriccurrent is passed through the cell, i.e. from the cathode through thecatholyte, the current-permeable partitionand the anolyte to the anode.Electrolytic cells of the required type and the methods of operatingthem are conventional and well known in the art, and such electrolyticcells and methods may be used in the process of this invention. Somesuitable apparatus and methods are described by S. Swann, Jr. in thechapter beginning on page 385 of Technique in Organic Chemistry, A.Weissberger, editor, Vol. II, 2nd ed. (1956), Interscience, N.Y., N.Y.;by Calingaert in US. Patent 1,539,297 by Mead in US. Patent 1,567,159;by Ziegler et al. in US. Patent 2,985,568; and by Foreman et al. in US.Patent 3,105,023.

The lead cathode may be in any form presenting a large surface for hightetraalkyl lead production, such as sheet, ribbon, rod or shot. By leadshot, it will be understood that small balls or pellets of lead aremeant, which usually will have diameters initially in the range of about0.05 to about 0.5 cm. The size of the pellets is not important so longas they are sufiiciently small for the purpose. With lead shot, goodelectrical contact is obtained by packing the particulate lead around asolid core of lead or other suitable electrode material which isattached to the potential source. The shot electrode is convenientlyhoused in a reticular plastic container through which catholyte solutioncan freely circulate. As reaction proceeds, the lead shot becomessmaller, eventually disappearing, and fresh make up shot is fed to thesystem to replace that consumed.

The anode, in general, may be made of any suitable electrode material,including lead, but usually will be of a different material. Sincehalogen (e.g. C1 Br I is produced in the anodic reaction, the anodeshould be resistant to corrosion by such halogen. Platinum is suitable,including Pt on Ti and Pt on Ta, and carbon may be used.

A variety of current-permeable membranes are known to the art and may beemployed as cell partitions in this process. It will be understood thatsuch materials may differ considerably in their resistance to the flowof ions as current-carriers and to the flow of non-ionics such as Water,nitrile solvent, and tetraalkyl lead. Suitable membrane materials areporous porcelain, asbestos, glass fiber paper, cellulosic substancessuch as porous cellophane and parchment, films of agar gel (supported onpolyethylene screen or porous glass, for example), films ofpolyurethanes, polyvinylidene fluoride, porous polyethylene, polyvinylbutyral, and ion exchange resins. Laminates of these materials may beused.

In general, the current-permeable membranes will permit Water to flowthrough them from an aqueous anolyte to a catholyte which is composedwholly or predominantly of organic compounds and contains only smallamounts of water. This transport of water through the membrane can occurin two ways: (a) by solution of the Water in and migration through themembrane, which is essentially a physicochemical phenomena highlydependent on membrane composition; (b) by streaming through pores orholes in the membrane wall, which is essentially a mechanical processand is largely independent of the membranes chemical make-up. Thus, themembranes can be characterized by water transport values. In general,the membranes have water transport values in the range 0.001 to 0.02gram of H 0 per sq. cm. of membrane area per minute under processconditions. Membranes with low water transport values, below about 0.003gram, are preferred in the process of this invention, as they permiteasier control of the water level in the catholyte.

Parchment paper, a preferred material, is preferably pretreated beforeuse with water or a solution of a tetraalkyl ammonium monohalide inWater for several hours at 20 C. to C. to increase its porosity anddecrease its electrical resistance, the tetraalkyl ammonium monohalidepreferably being selected from the class hereinbefore disclosed to besuitable for use as current-carriers in the catholyte and the anolyte.The parchment paper so treated is maintained in the wet porous stateuntil ready for use. Parchment paper so treated has a water transportvalue of about 0.002 gram of Water per squ. cm. per minute. Cationexchange resins, wherein the fixed anionic sites are carboxylate orsulfonate groups which may be in the free acid, alkali metal orquaternary ammonium salt form, constitute another preferred class. Whenthe cation exchange resin has alkali metal in its cationic sites, themetal may be replaced by tetraalkyl ammonium ions by ion-exchange duringthe process. While alkali metal is objectionable in the electrolytecompositions of this invention, the amount thereof so released from theresin normally is too small to produce significant adverse effects. Thepossibility of the introduction of objectionable amounts of alkali metalinto the electrolyte from such a resin can be greatly decreased oreliminated by pretreating the resin with a solution of a tetraalkylammonium monohalide so as to replace the alkali metal with thetetraalkyl ammonium ion. Water-treated parchment and the cation exchangematerials are preferred for their permselective characteristics. Theyretard passage of polyhalide ions from the anode compartment to thecathode compartment, said polyhalides being reactive towards tetraalkyllead, and of tetraalkyl lead from the cathode compartment to the anodecompartment Where it tends to be destroyed by reaction with polyhalideions.

The voltage applied to the cell is not critical so long as it issufficient to overcome the resistance of the cell (including that of thecatholyte, the anolyte and the cell membrane) and to reduce the alkylhalide at the cathode, thereby establishing current flow. Once the alkylhalide begins to be reduced, the cell with its components constitutes anelectrical conductor. Ohms law of electrical conductance states that themagnitude of the current flowing in a conductor is directly proportionalto the difference of potential between the ends of the conductor (herebetween the cathode and the anode) and is inversely proportional to itsresistance (here the total resistance, summing the resistances of allcomponent parts through which the current must pass). In a given cell ata given instant, the resistance is essentially a constant so that thecurrent is directly proportional to the applied potential, i.e. thepotential difference between the electrodes. Thus, the greater thepotential the more the current, and, with a given electrode geometry,the greater the current density at the electrode in question. Inprinciple, a desired current density can be maintained by applying aconstant voltage across the cell. In practice, however, the voltagerequirement often varies, primarily because cell resistance tends tochange during the course of the reaction as a result of changes (1) inthe bulk chemical constitution of the catholyte and/ or the anolyte, oreven of the cell membrane, and (2) at the electrode surfaces, sometimesreferred to as polarization phenomena which is related to the speedswith which reactants are replenished at the reacting surfaces and atwhich the reaction products difluse away from these sites.

The reduction of the alkylating agent requires about 1-2 volts, and,normally, the overall voltage is adjusted so that the potential at thecathode itself is suflicient to effect this reduction but does notgreatly exceed this minimum potential. The potential at the cathodeitself is conveniently measured with a probe electrode versus a standardelectrode, suitably a saturated calomel reference electrode, accordingto known techniques. Because of internal resistances, at least about 45volts are required for cell operation. Higher voltages, up to 35 voltsfor example, can be used, but it is seldom necessary to exceed about 20volts in the process of this invention.

Current densities of from about 0.05 to 0.5 amp./ sq. cm. of effectivecathode area may be employed, but more usually will be from about 0.1 toabout 0.4 amp./ sq. cm., most preferably about 0.2 amp./ sq. cm. Currentdensities of up to about 0.4 amp/sq. cm. have been employed. It issometimes necessary to employ current densities above the optimum as faras electrical yield is concerned in order to obtain a higher productionrate to meet a demand for the product. When a cathode is employed whichis formed of lead shot the potential diiference between the anode andthe cathode is greatest at the cathodes outermost surface, i.e. thatclosest to the anode. The outermost surface of such cathode can beregarded as being substantially smooth for calculating current density,that is the efiective area is approximately that of the outercylindrical surface of the body of lead shot.

Operating temperatures are normally from about C. to about 80 C.,consonant with a practical rate of production of the tetraalkyl leadcompound and the thermal stability of the system, preferably from about40 C. to about 50 C. The pressure should be at least suflicient tomaintain the catholyte and the anolyte in the liquid state at thetemperature of operation, but otherwise may be subatmospheric orsuperatmospheric, if desired. Usually, it will be preferred to employabout atmospheric pressure, when practicable. Reflux facilities may beused when necessary to retain volatile components in the system and toaid in controlling reaction temperatures. Also, if desired, an inertatmosphere, such as nitrogen, helium, argon or methane, may be employed.

The process may be operated batchwise. Usually, it will be necessary toadd further amounts of the currentcarrying tetraalkyl ammoniummonohalide and the hydroxylic compound to the catholyte and of thecurrentcarrying tetraalkyl ammonium monohalide to the anolyte during theelectrolysis so as to adjust and maintain the concentrations thereof inthe catholyte and in the anolyte within predetermined limits within theranges hereinbefore disclosed, in order to maintain efficient operationuntil the electrolysis is completed. Also, if large batches areinvolved, it usually will be necessary to periodically or continuouslyreplenish the lead cathode during the electrolysis so as to maintain theelfective area of cathode within reasonable limits. Means and methodsfor advancing a consumable electrode into electrical apparatus so as tomaintain a desired effective electrode area therein are conventional,well-known and may be used. Replenishment of the lead cathode isconveniently accomplished with a cathode formed of lead shot by merelyadding more lead shot thereto as may be necessary.

The process of this invention is particularly adapted for continuousoperation and it preferably is so operated. Such a continuous operationwill comprise:

(A) passing an electrolyzing direct electric current through the cell(B) while continuously recirculating through the cathode compartment astream of a liquid catholyte which initially consists essentially of'(a) an alkyl halide in which the alkyl group has 1- 10 carbon atoms andthe halogen atom has an atomic number of at least 17,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1- 18 carbonatoms and the halogen atom has an atomic number of at least 17, saidcurrent-carrier being in a concentration sufficient to provide acatholyte having a conductivity of at least 0.001 ohmcmr and (c) fromabout 1 to 20 moles per mole of said current-carrier of at least onehydroxylic compound of the class consisting of water and alkanols of l-4carbon atoms; and

(C) continuously recirculating through the anode compartment a stream ofa liquid anolyte which initially consists essentially of a solution of(l) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has l-18 carbonatoms and the halogen atom has an atomic number of at least 17, in aconcentration suflicient to provide an anolyte having a conductivity ofat least 0.001 ohrncm.-

(2) in an inert solvent having a reduction potential at least as high assaid alkyl halide and an oxidation potential higher than saidcurrent-carrier; and

(D) continuously withdrawing a portion of the catholyte from therecirculating catholyte stream that has passed through the cathodecompartment and (D adding to the recirculating catholyte stream beforeit reenters the cathode compartment additional amounts of said alkylhalide, current-carrier and hydroxylic compound as may be necessary toreplace those consumed in the electrolysis and those withdrawn and toprovide a recirculating catholyte stream entering the cathodecompartment which has those ingredients in desired concentrations andrelative proportions within the ranges specified in (a) to (c),inclusive;

(E) simultaneously withdrawing a portion of the anolyte from therecirculating anolyte stream that has passed through the anodecompartment and (E adding to the recirculating anolyte stream before itreenters the .anode compartment additional amounts of saidcurrent-carrier and said solvent as may be necessary to replace thoseconsumed in the electrolysis and those withdrawn and to provide arecirculating anolyte stream entering the anode compartment which has adesired conductivity of at least 0.001 ohm- CHI-.1; and

(F) recovering tetraalkyl lead from the withdrawn portion of thecatholyte.

The le-ad cathode will be replenished as may be necessary to maintain areasonably constant efiective cathode area. Also, in those operations inwhich there are formed tetraalkyl ammonium polyhalides which separatefrom the anolyte, such tetraalkyl amomnium polyhalides will be removedfrom the anode compartment continuously or periodically as may benecessary to avoid its accumulation therein to such an extent as toobjectionably decrease the volume of the anode compartment or tootherwise interfere with the effective operation of the cell.

Apparatus suitable for the continuous operation of the process of thisinvention and the methods of operating such apparatus are well known tothe art and are disclosed by S. Swann, Jr., Ziegler et a1. and Foremanet al., hereinbefore referred to.

One form of apparatus, which has been found to be particularly usefulfor the continuous operation of the process of this invention, isillustrated in vertical crosssection in the accompanying drawing as acell having an outer cylindrical anode, a central axially disposedcathode, and an intermediate cylindrical current-permeable membraneproviding an annular anode compartment and an inner cylindrical cathodecompartment. More specifically, the cell has an outer cylindrical shellof glass which has supported on its inner surface a cylindrical liner ortube 11 of platinum that serves as the anode. A cylindrical membrane 14is positioned about 0.5- cm. inwardly of the anode 11 and concentrictherewith and extends from top to bottom of the cell to divide the cellinto the anode compartment 12 and the cathode compartment 20. The shell10 is provided with an inlet (or outlet) 13a and an outlet (or inlet)13b connected to a source of circulating anolyte for the anodecompartment 12. The membrane 14 is composed of parchment paper about0.015 cm. thick.

The cathode is an assembly of (a) a lead (Pb) rod 15 having a diameterof about 0.32 cm. which is positioned axially of the cell and extendsvertically from the bottom of the cell to the horizontal plane of thetop of the anode 11; (b) cleaned lead shot 16, about 0.21 cm. indiameter packed around the rod 15, in good electrical contact with it,over a height vertically coextensive with the anode 11, and held inplace by (c) a vertical cylindrical reticulated screen 17 of 80 meshnylon extending from the bottom to the top of the cell, spaced about 0.5cm. from membrane 14, and having similar nylon mesh grid 18 supportingthe lead shot. The annular space between the screen 17 and the membrane14 constitutes a cathode compartment which is connected to a source ofcirculating catholyte through the screen 17, below and above the body oflead shot 16, and catholyte inlet (or outlet) 19a and catholyte outlet(or inlet) 19b. The inside area of the nylon cylinder 17, which iscoextensive with the body of lead shot 16, has an area of 103 sq. cm.which is taken as the effective area of the lead cathode.

The anode compartment 12 and the cathode compartment 20 are closed atthe bottom by an end plug 21 and at the top by a like end plug 22 whichare made of electrical insulating material and which serve to supportand position the membrane 14 and screen 17 within the cell. An inlet 23is provided at the top of the cell for charging the lead shot to thecathode assembly. The anode 11 and the cathode rod 15 are connected to asource of direct electric current through electrical leads 11a and 15a,respectively.

The cell is provided with a heat exchange jacket 24 which is connectedwith a source of circulating heat exchange fluid through inlet 24a andoutlet 24b.

It will be understood that the specific materials of the cell are thoseused, and that other suitable materials may be employed in their place.For example, the shell 10 may be made of other suitable inert materialswhich are nonconductive of electric current, and the anode 11 may be ofother suitable anode materials which are inert to the reactants. Otherforms of lead cathode may be employed. Also, the screen 17 and grid 18may be made of other reticulated material which is inert to thereactants employed and is non-conductive of electric current. Themembrane 14 may be made of other suitable membrane materials which arepermeable to electric current and ions, and which have been described inmore detail hereinbefore.

The catholyte product may be treated by various methods to recover thetetraalkyl lead compound therefrom. For example, it may be diluted witha large excess of water, the tetraalkyl lead extracted with ahydrocarbon solvent such as pentane, and then separated from the solventby fractional distillation under reduced pressure. Also, the catholyteproduct may be directly subjected to fractional distillation or steamdistillation according to known methods. With acetonitrile as thesolvent and tetra: methyl lead as the product, the catholyte productpreferably will be subjected to fractional distillation whereby thetetramethyl lead is obtained as a low-boiling azeotropic mixture withacetonitrile. Such azeotropic mixture consists essentially of about 61%by weight of tetramethyl lead and about 39% by weight of acetonitrileand boils at about 73 C. at atmospheric pressure and, on cooling to 25C. or below, separates into two phases, the upper phase being rich inacetonitrile and the lower phase being rich in tetramethyl lead. Thetetramethyl lead, in either phase, can be obtained free of acetonitrileby washing the mixture with water which dissolves the acetonitrile, thetetramethyl lead being insoluble in Water. When a volatile thermalstabilizer, e.g. benzene, toluene, or xylene, is present in thecatholyte composition, such material will co,- distill with thetetramethyl lead, alkanonitrile, and catholyte water, forming in effecta more complex azeotrope. The tetramethyl lead-hydrocarbon stabilizercomposition can be recovered ready for blending and free ofalkanonitrile by washing the distillate with water.

In order to more clearly illustrate this invention, presently preferredmethods of operating it, and the advantages to be obtained thereby, thefollowing examples are given in which the parts and proportions are byweight except where specifically indicated otherwise.

EXAMPLE 1 (A) Water-free run (control) (run 1) The electrolytic cell isof conventional structure and comprises essentially a lead cathode, aplatinum anode, and separate cathode and anode compartments separated bya dry parchment paper membrane. The cathode and anode compartments areeach charged with 25.2 parts (0.12 mole) of dry tetraethylammoniumbromide (Et NBr) and 260 parts of dry acetonitrile. Then 46.7 parts(0.49 mole) of methyl bromide (MeBr) are added to the catholyte solutionunder a dry nitrogen atmosphere. The cell is closed, the anolyte andcatholyte solutions are warmed to 45 C., and the direct current isturned on. Current is passed through the cell for 3.67 hours, duringwhich time the input voltage is adjusted to provide a constant currentdensity of about 0.06 amp./ sq. cm. and the temperature is maintained at45 C. The resulting catholyte composition contains tetramethyl lead(TML) in yields of 73% based on the current passed and 81% based on theweight of lead lost by the cathode during the run. These and otherpertinent data are included in the following summarizing Table I.

(B) Eifect of water (this invention) (runs 2-5) TABLE I.EFFECT OF H2O ONELECTROYLYTIC TML F0 RMATION Catholyte composition:

MeBr m0les/kg 1.411.47 EtiNBr do 0. 34-0. 36 HzO As below acetonitrilesolvent.

H O Content of Catholyte Molar Lowest Cell Percent 'IML Yield Run 2Voltage Percent by Moles/kg. EtiNBl' Elect. Pb-Loss Wt. 0 0 26 73 81 0.65 0. 36 ill 20 92 92 2. 5 1. 4 4/1 13 90 4. 9 2. 9 8/1 6. 4 87 91 9. 85. 8 17/1 4. 9 84 93 parts less acetonitrile in the catholyte.

The data show that the hydroxylic component affords a significantly moreefiicient system in terms of cell voltage requirement and product yield.

EXAMPLE 2 The electrolytic cell was similar to that of Example 1 and wasequipped with means for adding and removing catholyte and anolyteingredients. The cell partition was a cation exchange resin consistingessentially of a polyethylene backbone having pendant carboxyl groups inthe sodium form. The initial catholyte solution consisted of 6.66 parts(0.032 mole) of Et NBr, 69.1 parts of acetonitrile, and 13.7 parts(0.144 mole) of MeBr. A solution of 5.04 parts (0.024 mole) of Et NBr in52.1 parts of acetonitrile served as the initial anolyte. With thesolutions at 41 C., direct current flow was started. The voltage,initially at 6.5 volts corresponding to a current density of 0.025amp/sq. cm, was increased gradually over a period of 7 minutes to 16.5volts giving a current density of 0.1 amp./ sq. crn. At this point,vigorous gas evolution began in the cathode compartment. Methanol, 1.6

parts (0.05 mole), was added and the gassing ceased. After 4 moreminutes, with the current density at 0.125 amp./ sq. cm., obtained byincreasing the potential to 17.8 volts, slight gassing began which wassuppressed with a second 0.05 mole portion of methanol. The electrolysiswas continued with a current density at 0.15 amp/sq. cm., obtained byraising the applied voltage to about 18.7 volts, two more 0.05 moleadditions of methanol being made after 48 and 55 minutes of elapsedoperating time to suppress slight gassing. During the run, the cellvoltage requirement was kept below about volts by periodically replacinganolyte solution with fresh anolyte of the original composition toreplenish the supply of Et N+ and Br ions. The run was terminated after1 hour. The tetramethyl lead yield was 83% based on the current passed,and' 89% based on the Weight of lead consumed.

In summary, the starting catholyte composition contained 1.5 moles MeBrand 0.33 mole Et NBr per kilogram of solution. Each 0.05 molar MeOHaddition corresponded to 0.55 mole/kg. of solution and to a molarMeOH/Et NBr ratio of about 1.3/1, with the total amounting to about 2moles/kg. of solution and a molar ratio of MeOH/Et NBr of about 6/ 1. Itwill be apparent that the tetramethyl lead could not have "been obtainedas efliciently (83% electrical yield) in the absence of the methanol,because of the gas-forming side reactions that otherwise occur at thecurrent density level utilized.

For comparison, the procedure of Example 1 was repeated except thatmethanol in one run and ethanol in another replaced the acetonitrile ofboth the cathlyte and the anolyte solutions. With methanol, thetetraJnethyl lead yields were about 2% based on current and 69% based onPb consumed. With ethanol, the electrical yield was the Pb-loss yield92%. In both systems, considerable gassing occurred throughout the runsin agreement with the low electrical yields. Furthermore, the additionto these systems of water corresponding to about 1.4 moles/kg. ofcatholyte and to a molar H O/Et -NBr ratio of about 4/1 had nobeneficial effect on the tetramethyl lead yield or on the degree ofgassing. In these runs, the solvent quantities of the alcoholscorresponded to 24 moles MeOH and 17 moles EtOH per kilogram of solutionand to molar alcohol/Et NBr ratios of about 67/1 for MeOH and 47/1 forEtOH.

Thus, it is apparent that use of alcohol in solvent quantities(Calingaert U.S. Patent 1,539,297) is not the equivalent of the use ofthe limited amounts of hydroxylic compound used in this invention. Sincethese results obtained with the alcohol solvent-based systems are muchinferior to those obtained with the non-hydroxylic solvent system(control run 1 of Example 1), it is not obvious that use of an alcoholsuch as MeOH in limited amounts in the same non-hydroxylic solventsystem would result in an overall superior system for the electrolyticproduction of tetraalkyl lead (Example 2).

EXAMPLE 3 Equipment The apparatus shown in the drawing and described indetail hereinbefore.

The Pb shot was cleaned by washing with aqueous (0.515%) HNO rinsedacid-free with water, rinsed with acetone and dried by evaporation, andstored under N before use.

The parchment paper membrane, in place in the cell, was conditioned bycontacting it with boiling water for 0.5-2 hours. The water was drainedand then the cathode compartment was filled with an acetonitrilesolution of 7.5% Et NBr and 4% H O, the nylon cylinder was charged withclean Pb shot, and the anode compartment was filled with Watercontaining 5% Et NBr. The condi tioned membrane can be kept indefinitelyunder these conditions.

Start-up The cell was drained. A feed consisting of 15% CH Br (1.58moles/kg), 7.5% Et NBr (0.33 mole/kg), 1% H O (0.56 mole/kg.) and 76.5%acetonitrile was circulated through the cathode chamber at a rate of1500 mL/min. and at 42 C. At the same time, a fresh 5% Et NBr-H Osolution at 45 C. was circulated through the anode compartment at aboutthe same rate. While under circulation, catholyte solution wascontinually withdrawn from the circulating stream and fresh solutionadded at the rate of 15 ml./min. Circulation of the feed stocks wascontinued, without the application of electric current, until the H 0content of the cathode chamber solution reached a steady state of 4.5%(2.5 moles/kg.) as a result of H 0 transport across the membrane fromthe anode side, in about 45 minutes.

Electrolysis At this point, in an attempt to compensate for thetransport of anode water and maintain the Water content of thecirculating catholyte solution approximately constant, the water levelin the fresh catholyte feed solution was decreased to 0.2% (0.11mole/kg). At the same time, the direct current was turned on. Thecurrent densitywas increased over a 0.25 hr. period to 0.18 amp/sq. cm.with a cell voltage of 11.3 volts. As a result, the temperature of thecatholyte solution slowly rose to about 45 C.

The flow of a 30% Et NBr-H O solution was begun into the circulatinganolyte composition at a rate of 5.8 g./min., while a portion of thetotal-was simultaneously removed at a rate of 3.6 g./min., in order tocompensate for the depletion of the electrolyte as the result of (a)transport of Et N across the membrane to the cathode side and (b)formation on the anode side of tetraethylammonium polybromide whichseparated as a water-immiscible layer as the electrolysis progressed andwhich was removed from time to time.

After 1.5 hours, the cell voltage required for maintain- 1? ing thecurrent density at 0.18 amp/sq. cm. had risen to 12.5 volts and thewater content of the catholyte solution had dropped from 4.5% (2.5moles/kg.) to 3.5% (1.95 moles/kg). Water was then added to thecatholyte solution as needed to maintain a 5% level (2.7-8 moles/kg.)and a voltage of 11.4-11.5 volts. After 2.33 hours of operation, duringwhich time the Et NBr content of the catholyte had increased to about11% (0.52 mole/kg), the electrolysis was terminated.

The tetramethyl lead yield was 92% based on the total current passedthrough the cell, and 95% based on the weight of lead lost by thecathode during the electrolysis.

EXAMPLE 4 The electrolytic cell is similar to that of Example 1 andcomprises a lead cathode, platinum anode, and cathode and anodecompartments separated by a parchment paper membrane. The cathode andanode compartments are equipped with a reflux condenser for methylbromide. The archment paper membrane had been soaked overnight in water;excess water was allowed to drain away just before the membrane wasplaced in the cell for immersion in the electrolyte solution. To eachcompartment was added a cold (about 8 C.) solution consisting of 75%MeBr, 20% tetra-n-butyl ammonium bromide and 5% water, all by weight,the Bu NBr concentration corresponding to 0.62 gm.-mole/kg. of catholyteand anolyte and the molar ratio of water to Bu NBr being 4.5 1. Underthese conditions at 6 C.l C., a small amount of a white solid,apparently a MeBr hydrate, was present in the electrolyte composition.

The current was turned on. Little current flowed until the voltage wasraised from an initial 10 volts to 20 volts, when the current densityrose sharply from 0.001 amp/sq. cm. to 0.01 amp/sq. cm., then graduallyto 0.015 amp/sq. cm. over a minute period. The voltage was raised to 25volts, held there for about 8 minutes to give a steady current densityof 0.02 amp./ sq. cm., and then increased to 30 volts for a currentdensity of 0.03 amp./sq. cm. which was maintained for 40 minutes. MeBr,amounting to about A of the initial amount, was allowed to evaporatefrom the cell over a 5 minute period, whereupon the current density roseto 0.075 -amp./ sq. cm. at 30 volts. The reaction mixture was held for10 minutes at 0.075 amp./ sq. cm. and 30 volts. At this point, thetetramethyl lead con-- tent of the catholyte corresponded to a yield of79% based on the total current passed.

In comparison, when water was omitted from the anolyte and catholyte anddry parchment was used as the membrane, the maximum attainable currentdensity was about 0.012 amp/sq. cm., which corresponds to a lowerproduction rate, and the tetramethyl lead yield was 73% based oncurrent.

EXAMPLE 5 The cell is of the sandwich type with a lead cathode and aplatinum anode at a cell length of 1.0 cm., a cell partition area of 20cm. and means for circulating catholyte and anolyte through thecathode'and anode compartments.

The membrane is that designated as AMF ion number C-103-DD by theAmerican Machine and Foundry C0. and characterized as having an averageresistance in KCl solution of 6.0-7.0 ohm/cmP, a wet thickness of 6mils, and a 10% gel water. It has a high density polyethylene backbonewhich has been grafted with styrene and subsequently sulfonated toprovide a cation exchange material of the sulfonic acid type. For use inthis cell, the film is soaked for several hours in anolyte solutionconsisting of 7.5% by weight of Et NBr in water.

1000 grams of an anolyte solution, consisting of 7.5% by weight Et NBrin H O, is circulated and recycled continuously through the cell. 100grams of a catholyte solution, consisting of by weight MeBr, 7.5% EtNBr, 0.7% H 0, the rest acetonitrile (providing a molar H O/Et NBr ratioof about 1/ 1), is circulated through the cathode compartment, with aportion being removed at the outlet end at the rate of 6 grams/min.while fresh catholyte is added at the same rate at the inlet end of thecell. Cell temperature is maintained at 45 C, Under these conditions,the water permeation rate through the membrane is 8.2 mg./cm. /min., andthe acetonitrile permeation rate is 0.008 mg./cm. /min.

The current is turned on and the current density adjusted to O.lamp./cm.at a potential of 7 volts. After two hours, the water concentration inthe catholyte has increased to about 4%. The tetramethyl lead yield is92% based on current passed, and 95 based on the Pb consumed from thecathode.

It will be understood that the foregoing examples and the drawing havebeen given for illustrative purposes solely, and that this invention isnot limited to the specific embodiments described and shown therein. Onthe other hand, it will be readily apparent to those skilled in the artthat, subject to the limitations set forth in the general description,many variations can be made in the materials, proportions, conditions,techniques and apparatus employed without departing from the spirit orscope of this invention.

From the foregoing description, it will be apparent that this inventionprovides a new and improved process for producing tetraalkyl leadcompounds. It constitutes a material improvement over the priorprocesses, overcoming problems involved in the prior processes, resultsin higher yields of tetraalkyl lead compounds, and makes it possible toproduce the tetraalkyl lead compounds at much higher rates. It is simpleand economical to operate and particularly it enables ready control ofthe conditions so that the production of tetraalkyl lead compounds canbe maintained at maximum efiiciency throughout the electrolysis.Especially, it provides a continuous process which can be operated overlong periods of time at high efiiciency with high yields of tetraalkyllead compounds at high rates of production, maximum utilization ofmaterials, minimum expenditures of energy, and low costs. It is believedto be the first commercially feasible electrolytic process for producingtetraalkyl lead antiknock compounds. Accordingly, it will be apparentthat this invention constitutes an important and valuable advance in andcontribution to the art.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An electrolytic process for producing tetraalkyl lead compounds at alead cathode in an electrolytic cell having a lead cathode, an anode ofa material which is resistant to attack by halogens of atomic numbers 17to 53, and a current-permeable partition separating the catholyte fromthe anolyte, which process comprises (A) passing an electrolyzing directelectric current through (B) a liquid catholyte which initially consistsessentially (a) an alkyl halide in which the alkyl group has 1-10 carbonatoms and the halogen atom has an atomic number of at least 17,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has l-18 carbonatoms and the halogen atom has an atomic number of at least 17, saidcurrent-carrier being in a concentration sufficient to provide acatholyte having a conductivity of at least 0.001 ohmcm. and

(c) from about 1 to 20 moles per mole of said current-carrier of atleast one hydroxylic compound of the class consisting of water andalkanols of 14 carbon atoms; and

(C) a liquid anolyte which initially consists essentially of a solutionof (1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl groups has 118 carbonatoms and the hlaogen atom has an atomic number of at least 17, in aconcentration sufiicient to provide an anolyte having a conductivity ofat least 0.001 ohm Gilli 2) in an inert solvent having a reductionpotential at least as high as said alkyl halide and an oxidationpotential higher than said currentcarrier;

(D) during the electrolysis, adjusting the amounts of thecurrent-carrier in the catholyte and the anolyte as may be necessary tomaintain their conductivities at at least 0.001 ohm cm. and adjustingthe amount of the hydroxylic compound in the catholyte as may benecessary to maintain the concentration thereof within the range of fromabout 1 to about moles per mole of said current-carrier; and

(E) recovering tetraalkyl lead from the catholyte.

2. An electrolytic process for producing tetraalkyl lead compounds at alead cathode in an electrolytic cell having a lead cathode, an anode ofa material which is resistant to attack by halogens of atomic numbers 17to 53, and a current-permeable partition separating the catholyte fromthe anolyte, which process comprises (A) passing an electrolyzing directelectric current through (B) a liquid catholyte which initially consistsessentially of (a) an alkyl bromide in which the alkyl group has 1-10carbon atoms,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction po tentialthan said alkyl bromide and in which each alkyl group has 1-18 carbonatoms, said current-carrier being in a concentration suflicient toprovide a catholyte having a conductivity of at least 0.001 ohm cm.- and(c) from about 1 to 20 moles of water per mole of said current-carrier;and

(C) a liquid anolyte which initially consists essentially of a solutionof (1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan said alkyl bromide and in which each alkyl group has 1-18 carbonatoms, in a concentration sutficient to provide an anolyte having aconductivity of at least 0.001 ohmcmr (2) in water;

(D) during the electrolysis, adjusting the amounts of thecurrent-carrier in the catholyte and the anolyte as may be necessary tomaintain their conductivities at at'least 0.001 ohmcm.- and adjustingthe amount of the water in the catholyte as may be necessary to maintainthe concentration thereof within the range of from about 1 to about 20moles per mole of said current-carrier; and

(E) recovering tetraalkyl lead from the catholyte.

3. An electrolytic process for producing tetraalkyl lead compounds at alead cathode in an electrolytic cell having a lead cathode, an anode ofa material which is resistant to attack by halogens of atomic numbers 17to 53, and a current-permeable partition separating the catholyte fromthe anolyte, which process comprises (A) passing an electrolyzing directelectric current through (B) a liquid catholyte which initially consistsessentially of (a) an alkyl bromide of l-2 carbon atoms,

'(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction po- 20 tten-tial than said alkyl bromide and in which each alkyl group has 1-2carbon atoms, said current-carrier being in a concentration sufiicientto provide a catholyte having a conductivity of at least 0.01 ohmcmf and(c) from about 3 to about 10 moles of water per mole of saidcurrent-carrier; and

(C) a liquid anolyte which initially consists essentially of a solutionof (1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which hasa higher reduction potentialthan said alkyl bromide and in which each alkyl group has 12 carbonatoms, in a concentration suflicient to provide an anolyte having aconductivity of at least 0.01 ohm cmf (2) in water;

(D) during the electrolysis, adjusting the amounts of thecurrent-carrier in the catholyte and the anolyte as may be necessary tomaintain their conductivities at at least 0.01 ohm cmr and adjusting theamount of the water in the catholyte as may be necessary to maintain theconcentration thereof within the range of from about 3 to about 10 molesper mole of said current-carrier; and

(E) recovering tetraalkyl lead from the catholyte.

4. An electrolytic process for producing tetraalkyl lead compounds at alead cathode in an electrolytic cell having a lead cathode, an anode ofa material which is resistant to attack by halogens of atomic numbers 17to 53, and a current-permeable partition separating the catholyte fromthe anolyte, which process comprises (A) passing an electrolyzing directelectric current through (B) a liquid catholyte which initially consistsessentially of (a) from about 0.1 to about 3 gram moles per kilogram ofcatholyte of an alkyl halide in which the alkyl group has l-IO carbonatoms and the halogen atom has an atomic number of at least 17,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1-18 carbonatoms and the halogen atom has an atomic number of at least 17, saidcurrent-carrier being in a concentration sufiicient to provide acatholyte having a conductivity of at least 0.001 ohmcm.- and (c) fromabout 1 to 20 moles per mole of said current-carrier of at least onehydroxylic compound of the class consisting of water and alkanols of 1-4carbon atoms,

(d) the rest of the catholyte consisting essentially of an inertnonhydroxylic organic solvent for both said alkyl halide and saidcurrent-carrier which solvent has a reduction potential higher than saidalkyl halide and an oxidation potential higher than saidcurrent-carrier; and

(C) a liquid anolyte which initially consists essentially of a solutionof (1) a current-carrier which consists of at least one current-carryingtetra-alkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1-18 carbonatoms and the halogen atom has an atomic number of at least 17, in aconcentration sufficient to provide an anolyte having a conductivity ofat least 0.001 ohmcmr (2) in an inert solvent having a reductionpotential at least as high as said alkyl halide and an oxidationpotential higher than said current-carner- (D) during the electrolysis,adjusting the amounts of the current-carrier in the catholyte and theanolyte as may be necessary to maintain their conductivities at at least0.001 ohmcm.- and adjusting the amount of the hydroxylic compound in thecatholyte as may be necessary to maintain the concentration thereofWithin the range of from about 1 to about 20 moles per mole of saidcurrent-carrier; and

(E) recovering tetraalkyl lead from the catholyte.

5. An electrolytic process for producing tetraalkyl lead compounds at alead cathode in an electrolytic cell having a lead cathode, an anode ofa material which is resistant to attack by halogens of atomic numbers 17to 53, and a current-permeable partition separating the catholyte fromthe anolyte, which process comprises (A) passing an electrolyzing directelectric current through (B) a liquid catholyte which initially consistsessentially of (a) from about 0.1 to about 3 gram moles per kilogram ofcatholyte of an alkyl halide in which the alkyl group has 1-2 carbonatoms and the halogen atom has an atomic number of at least 17,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1-2 carbonatoms and the halogen atom has an atomic number of at least 17, saidcurrent-carrier being in a concentration sutficient to provide acatholyte having a conductivity of at least 0.001 ohrncmf and (c) fromabout 1 to 20 moles per mole of said current-carrier of at least onehydroxylic compound of the class consisting of Water and alkanols of 1-4carbon atoms,

(d) the rest of the catholyte consisting essentially of at least onealkanonitrile in which the alkyl group has 1-5 carbon atoms; and

(C) a liquid anolyte which initially consists essentially of a solutionof (1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1-18 carbonatoms and the halogen atom has an atomic number of at least 17 in aconcentration suflicient to provide an anolyte having a conductivity ofat least 0.001 ohmcmr (2) in an inert solvent having a reductionpotential at least as high as said alkyl halide and an oxidationpotential higher than said current-carrier;

(D) during the electrolysis, adjusting the amounts of thecurrent-carrier in the catholyte and the anolyte as may be necessary tomaintain their conductivities at at least 0.001 ohm and CH1.1 andadjusting the amount of the hydroxylic compound in the catholyte as maybe necessary -to maintain the concentration thereof within the range offrom about 1 to about 20 moles per mole of said current-carrier; and

(E) recovering tetraalkyl lead from the catholyte.

6. An electrolytic process for producing tetraalkyl lead compounds at alead cathode in an electrolytic cell having a lead cathode, an anode ofa material which is resistant to attack by halogens of atomic numbers 17to 53, and a current-permeable partition separating the catholyte fromthe anolyte, which process comprises (A) passing an electrolyzing directelectric current through (B) a liquid catholyte which initially consistsessentially of (a) from about 1 to about 2 gram moles per kilogram ofcatholyte of an alkyl bromide in which the alkyl group has 1-2 carbonatoms,

(b) from about 0.25 to about 0.5 gram mole per kilogram of catholyte ofa current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan said alkyl bromide and in which each alkyl group has 12 carbonatoms,

(c) from about 3 to about 10 moles of water per mole of saidcurrent-carrier,

(d) the rest of the catholyte consisting essentially of acetonitrile;and

(C) a liquid anolyte which initially consists essentially of a solutionof (1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan said alkyl bromide and in which each alkyl group has 1-2 carbonatoms, in a concentration of from about 2% to about 20% by weight (2) inwater;

(D) during the electrolysis, adjusting the amounts of saidcurrent-carrier and water in the catholyte and the amount of saidcurrent-carrier in the anolyte as may be necessary to maintain theconcentrations thereof in the catholyte and in the anolyte within theranges specified in (b), (c) and (1), respectively; and

(E) recovering tetraalkyl lead from the catholyte.

7. An electrolytic process for producing tetramethyl lead at a leadcathode in an electrolytic cell having a lead cathode, an anode of amaterial which is resistant to attack by halogens of atomic numbers 17to 53, and a current-permeable partition separating the catholyte fromthe anolyte, which process comprises (A) passing an electrolyzing directelectric current through (B) a liquid catholyte which initially consistsessentially of (a) from about 1 to about 2 gram moles of methyl bromideper kilogram of catholyte,

(b) from about 0.25 to about 0.5 gram mole per kilogram of catholyte ofa current-carrier which consists of tetraethyl ammonium monobromide,

(c) from about 3 to about 10 moles of water per mole of saidcurrent-carrier,

(d) the rest of the catholyte consisting essentially of acetonitrile;and

(C) a liquid anolyte which initially consists essentially of a solutionof (l) a current-carrier which consists of tetraethyl ammoniummonobromide in a concentration of from about 5% to about 10% by weight(2) in acetonitrile;

(D) during the electrolysis, adjusting the amounts of saidcurrent-carrier and water in the catholyte and the amount of saidcurrent-carrier in the anolyte as may be necessary to maintain theconcentrations thereof in the catholyte and in the anolyte within theranges specified in (b), (c) and (1), respectively; and

(E) recovering tetramethyl lead from the catholyte.

8. An electrolytic process for producing tetramethyl lead at a leadcathode in an electrolytic cell having a lead cathode, an anode of amaterial which is resistant to attack by halogens of atomic numbers 17to 53, and a current-permeable partition separating the catholyte fromthe anolyte, which process comprises (A) passing an electrolyzing directelectric current through (B) a liquid catholyte which initially consistsessentially of (a) from about 1 to about 2 gram moles of methyl bromideper kilogram of catholyte, (b) from about 0.25 to about 0.5 gram moleper kilogram of catholyte of a current-carrier which consists oftetraethyl ammonium monobromide,

(c) from about 3 to about 10 moles of water per mole of saidcurrent-carrier,

(d) the rest of the catholyte consisting essentially of acetonritile;and

(C) a liquid anolyte which initially consists essentially of a solutionof (1) a current-carrier which consists of tetraethyl ammoniummonobromide in a concentration of from about 5% to about by weight (2)in water;

(D) during the electrolysis, adjusting the amounts of saidcurrent-carrier and water in the catholyte and the amount of saidcurrent-carrier in the anolyte as may be necessary to maintain theconcentrations thereof in the catholyte and in the anolyte within theranges specified in (b), (c) and (1), respectively; and

(E) recovering tetramethyl lead from the catholyte.

9. A continuous process for the electrolytic production of tetraalkyllead compounds at a lead cathode in an electrolytic cell having a leadcathode, an anode of a material which is resistant to attack by halogensof atomic numbers 17 to 53, and a current-permeable partition separatingthe cell into a cathode compartment and an anode compartment, whichprocess comprises (A) passing an electrolyzing direct electric currentthrough the cell (B) while continuously recirculating through thecathode compartment a stream of a liquid catholyte which initiallyconsists essentially of (a) an alkyl halide in which the alkyl group has1-10 carbon atoms and the halogen atom has an atomic number of at least17,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has l-18 carbonatoms and the halogen atom has an atomic number of at least 17, saidcurrent-carrier being in a concentration suflicient to provide acatholyte having a conductivity of at least 0.001 ohm cmf and (c) fromabout 1 to 20 moles per mole of said current-carrier of at least onehydroxylic compound of the class consisting of water and alkanols of 1-4carbon atoms; and

(C) continuously recirculating through the anode compartment a stream ofa liquid anolyte which initially consists essentially of a solution of(1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1l8 carbonatoms and the halogen atom has an atomic number of at least 17, in aconcentration suflicient to provide an anolyte having a conductivity ofat least 0.001 ohm cmf (2) in an inert solvent having a reductionpotential at least as high as said alkyl halide and an oxidationpotential higher than said currentcarrier; and

(D) continuously withdrawing a portion of the catholyte from therecirculating catholyte stream that has passed through the cathodecompartment and (D adding to the recirculating catholyte stream beforeit reenters the cathode compartment additional amounts of said alkylhalide, currentcarrier and hydroxylic compound as may be necessary toreplace those consumed in the electrolysis and those withdrawn and toprovide a recirculating catholyte stream entering the cathodecompartment which has those ingredients in desired concentrations andrelative proportions within the ranges specified in (a) to (c),inelusive;

(E) simultaneously withdrawing a portion of the anolyte from therecirculating anolyte stream that has passed through the anodecompartment and (E adding to the recirculating anolyte stream before itreenters the anode compartment'additional amounts of saidcurrent-carrier and solvent as may be necessary to replace thoseconsumed in the electrolysis and those withdrawn and to provide arecirculating anolyte stream entering the anode compartment which has aconductivity of at least 0.001 ohm cmf and (F) recovering tetraalkyllead from the withdrawn portion of the catholyte.

10. A continuous process for the electrolytic production of tetraalkyllead compounds at a lead cathode in an electrolytic cell having a leadcathode, an anode of a material which is resistant to attack by halogensof atomic numbers 17 to 53, and a current-permeable partition separatingthe cell into a cathode compartment and an anode compartment, whichprocess comprises (A) passing an electrolyzing direct electric currentthrough the cell (B) while continuously recirculating through thecathode compartment a stream of a liquid catholyte which initiallyconsists essentially of (a) from about 0.1 to about 3 gram moles perkilogram of catholyte of an alkyl halide in which the alkyl group has1-10 carbon atoms and the halogen atom has an atomic number of at least17,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1-18 carbonatoms and the halogen atom has an atomic number of at least 17, saidcurrent-carrier being in a concentration sufiicient to provide acatholyte having a conductivity of at least 0.001 ohm cmf and (c) fromabout 1 to 20 moles per mole of said current-carrier of at least onehydroxylic compound of the class consisting of water and alkanols of 1-4carbon atoms,

(d) the rest of the catholyte consisting essentially of an inertnonhydroxylic organic solvent for both said alkyl halide and saidcurrent-carrier which solvent has a reduction potential higher than saidalkyl halide and an oxidation potential higher than saidcurrent-carrier; and

(C) continuously recirculating through the anode com partment a streamof a liquid anolyte which initially consists essentially of a solutionof (1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1-18 carbonatoms and the halogen atom has an atomic number of at least 17 in aconcentration sutficient to provide an anolyte having a conductivity ofat least 0.001 ohm cmr (2) in an inert solvent having a reductionpotential at least as high as said alkyl halide and an oxidationpotential higher than said current-carrier; and

(D) continuously withdrawing a portion of thecatholyte from therecirculating catholyte stream that has passed through the cathodecompartment and (D adding to the recirculating catholyte stream beforeit reenters the cathode compartment additional amounts of said alkylhalide, currentcarrier, hydroxylic compound and solvent as may benecessary to replace those consumed in the electrolysis and thosewithdrawn and to provide a recirculating catholyte stream entering thecathode compartment which has those ingredients in desiredconcentrations and relative proportions within the ranges specified in(a) to (d), inclusive;

(E) simultaneously withdrawing a portion of the anolyte from therecirculating anolyte stream that has passed through the anodecompartment and (E adding to the recirculating anolyte stream before itreenters the anode compartment additional amounts of saidcurrent-carrier and solvent as may be necessary to replace thoseconsumed in the electrolysis and those withdrawn and to provide arecirculating anolyte stream entering the anode compartment which has aconductivity of at least 0.001 ohm cm. and

(F) recovering tetraalkyl lead from the withdrawn portion of thecatholyte.

11. A continuous process for the electrolytic production of tetraalkyllead compounds at a lead cathode in an electrolytic cell having a leadcathode, an anode of a material which is resistant to attack by halogensof atomic numbers 17 to 53, and a current-permeable partition separatingthe cell into a cathode compartment and an anode compartment, whichprocess comprises (A) passing an electrolyzing direct electric currentthrough the cell (B) while continuously recirculating through thecathode compartment a stream of a liquid catholyte which initiallyconsists essentially of (a) from about 0.1 to about 3 gram moles perkilogram of catholyte of an alkyl bromide in which the alkyl group has110 carbon atoms,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan said alkyl bromide and in which each alkyl group has 1-18 carbonatoms, said currentcarrier being in a concentration sufiicient toprovide a catholyte having a conductivity of at least 0.01 ohm cmf and(c) from about 1 to 20 moles of water per mole of said current-carrier,

(d) the rest of the catholyte consisting essentially of at least onealkanonitrile in which the alkyl group has 15 carbon atoms; and

' C) continuously recirculating through the anode compartment a streamof a liquid anolyte which initially consists essentially of a solutionof (1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan said alkyl bromide and in which each alkyl Y group has 1-18 carbonatoms, in a concentration sut'ricient to provide an anolyte having aconductivity of at least 0.01 ohm cm. (2) in at least one solvent of thegroup consisting of water, an alkanol of 1-4 carbon atoms, and analkanonitrile in which the alkyl group has 1-5 carbon atoms; and (D)continuously withdrawing a portion of the catholyte from therecirculating catholyte stream that has passed through the cathodecompartment and (D adding to the recirculating catholyte stream beforeit reenters the cathode compartment additional amounts of said alkylbromide, currentcarrier, water and alkanonitrile as may be necessary toreplace those consumed in the electrolysis and those withdrawn and toprovide a recirculating catholyte stream entering the cathodecompartment which has those ingredients in desired concentrations andrelative proportions within the ranges specified in (a) to (d),inelusive;

(E) simultaneously withdrawing a portion of the anolyte from therecirculating anolyte stream that has passed through the anodecompartment and (E adding to the recirculating anolyte stream before itreenters the anode compartment additional amounts of saidcurrent-carrier and solvent as may be necessary to replace thoseconsumed in the electrolysis and those withdrawn and to provide arecirculating anolyte stream entering the anode compartment which has aconductivity of at least 0.01 ohm GEL-'1; and

(F) recovering tetraalkyl lead from the withdrawn portion of thecatholyte.

127 A continuous process for the electrolytic production of tetraalkyllead compounds at a lead cathode in an electrolytic cell having a leadcathode, an anode of a material Which is resistant to attack by halogensof atomic numbers 17 to 53, and a current-permeable partition separatingthe cell into a cathode compartment and an anode compartment, whichprocess comprises (A) passing an electrolyzing direct electric currentthrough the cell (B) while continuously recirculating through thecathode compartment a stream of liquid catholyte which initiallyconsists essentially of (a) from about 1 to about 2 gram moles perkilogram of catholyte of an alkyl bromide in which the alkyl group has1-2 carbon atoms,

(b) from about 0.25 to about 0.5 gram mole per kilogram of catholyte ofa current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan said alkyl bromide and in which each alkyl group has 1-2 carbonatoms,

(c) from about 3 to about 10 moles of water per mole of saidcurrent-carrier,

(d) the rest of the catholyte consisting essentially of at least onealkanonitrile in which the alkyly group has 1-5 carbon atoms; and

(C) continuously recirculating through the anode compartment a stream ofa liquid anolyte which initially consists essentially of a solution of(1) a currentcarrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan said alkyl bromide and in which each alkyl group has 12 carbonatoms, in a concentration of from about 5% to about 10% by weight (2) inwater; and

(D) continuously withdrawing a portion of the catholyte from therecirculating catholyte stream that has passed through the cathodecompartment and (D adding to the recirculating catholyte stream beforeit reenters the cathode compartment additional amounts of said alkylbromide, currentcarrier, water and alkanonitrile as may be necessary toreplace those consumed in the electrolysis and those withdrawn and toprovide a recirculating catholyte stream entering the cathodecompartment which has those ingredients in desired relative proportionswithin the ranges specified in (a) to (d), inclusive;

(E) simultaneously withdrawing a portion of the anolyte from therecirculating anolyte stream that has passed through the anodecompartment and (E adding to the recirculating anolyte stream before itrenters the anode compartment additional amounts of said current-carrierand water as may be necessary to replace those consumed in theelectrolysis and those withdrawn and to provide a recirculating anolytestream entering the anode compartment which has those in- 27 gredientsin desired relative proportions within the ranges specified in (l) and(2); and

(F) recovering tetraalkyl lead from the Withdrawn portion of thecatholyte.

13. A continuous process for the electrolytic production of tetramethyllead at a lead cathode in an electrolytic cell having a lead cathode, ananode of a material which is resistant to attack by halogens of atomicnumbers 17 to 53, and a current-permeable partition separating the cellinto a cathode compartment and an anode compartment, which processcomprises (A) passing an electrolyzing direct electric current throughthe cell (B) while continuously recirculating through the cathodecompartment a stream of a liquid catholyte which initially consistsessentially of (a) from about 0.1 to about 3 gram moles of methylbromide per kilogram of catholyte, (b) a current-carrier which consistsof at least one current-carrying tetraalkyl ammonium monobromide whichhas a higher reduction potential than methyl bromide and in which eachalkyl group has 1-18 carbon atoms, said current-carrier being in aconcentration sufficient to provide catholyte having a conductivity ofat least 0.01 ohm cm. and

(c) from about 1 to 20 moles of water per mole of said current-carrier,

(d) the rest of the catholyte consisting essentially of an inertnonhydroxylic organic solvent for 'both methyl bromide and saidcurrent-carrier which solvent has a reduction potential higher thanmethyl bromide and an oxidation potential higher than saidcurrent-carrier; and

(C) continuously recirculating through the anode compartment a stream ofa liquid anolyte which initially consists essentially of a solution of(l) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan methyl bromide and in which each alkyl group has 1-18 carbon atoms,in a con centration sutiicient to provide an anolyte having aconductivity of at least 0.01 ohmcmr (2) in an inert solvent having areduction potential at least as high as methyl bromide and an oxidationpotential higher than said current-carrier;

(D) continuously withdrawing a portion of the catholyte from therecirculating catholyte stream that has passed through the cathodecompartment and (D adding to the recirculating catholyte stream beforeit reenters the cathode compartment additional amounts of said methylbromide, currentcarrier, water and solvent as may be necessary toreplace those consumed in the electrolysis and those withdrawn and toprovide a recirculating catholyte stream entering the cathodecompartment which has those ingredients in desired concentrations andrelative proportions within the ranges specified in (a) to (d),inelusive;

(E) simultaneously withdrawing a portion of the anolyte from therecirculating anolyte stream that has passed through the anodecompartment and (E adding to the recirculating anolyte stream before itreenters the anode compartment additional amounts of saidcurrent-carrier and solvent as may be necessary to replace thoseconsumed in the electrolysis and those Withdrawn and to provide arecirculating anolyte stream entering the anode compartment which has aconductivity of at least 0.01 ohm cm.- and (F) recovering tetramethyllead from the Withdrawn portion of the catholyte.

14. A continuous process for the electrolytic production of tetramethyllead at a lead cathode in an electrolytic cell having a lead cathode, ananode of a material which is resistant to attack by halogens of atomicnumbers 17 to 53, and a current-permeable partition separating the cellinto a cathode compartment and an anode compartment, which processcomprises (A) passing an electrolyzing direct electric current throughthe cell (B) while continuously recirculating through the cathodecompartment a stream of a liquid catholyte which initially consistsessentially of (a) from about 1 to about 2 gram moles of methyl bromideper kilogram of catholyte,

(b) from about 0.25 to about 0.5 gram mole per kilogram of catholyte ofa current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan methyl bromide and in which each alkyl group has 1-2 carbon atoms,

(c) from about 3 to about 10 moles of water per mole of saidcurrent-carrier,

(d) the rest of the catholyte consisting essentially of at least onealkanonitrile in which the alkyl group has l-5 carbon atoms; and

(C) continuously recirculating through the anode compartment a stream ofa liquid anolyte which initially consists essentially of a solution of(1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan methyl bromide and in which each alkyl group has 1-2 carbon atoms,in a concentration of from about 5% to about 10% by weight (2) in water;and

(D) continuously withdrawing a portion of the catholyte from therecirculating catholyte stream that has passed through the cathodecompartment and (D adding to the recirculating catholyte stream beforeit reenters the cathode compartment additional amounts of said methylbromide, current-carrier, water and alkanonitrile as may be necessary toreplace those consumed in the electrolysis and those withdrawn and toprovide a recirculating catholyte stream entering the cathodecompartment which has those ingredients in desired relative proportionswithin the ranges specified in (a) to (d), inclusive;

(E) simultaneously withdrawing a portion of the anolyte from therecirculating anolyte stream that has passed through the anodecompartment and (E adding to the recirculating anolyte stream before itreenters the anode compartment additional amounts of saidcurrent-carrier and water as may be necessary to replace those consumedin the electrolysis and those withdrawn and to provide a recirculatinganolyte stream entering the anode compartment which has thoseingredients in desired relative proportions within the ranges specifiedin (1) and (2); and

(F) recovering tetramethyl lead from the withdrawn portion of thecatholyte.

15. A continuous process for the electrolytic production of tetramethyllead at a lead cathode in an electrolytic cell having a lead cathode, ananode of a material which is resistant to attack by halogens of atomicnumbers 17 to 53, and a current-permeable partition separating the cellinto a cathode compartment and an anode compartment, which processcomprises (A) passing an electrolyzing direct electric current throughthe cell (B) While continuously recirculating through the cathodecompartment a stream of a liquid catholyte which initially consistsessentially of (a) from about 0.1 to about 3 gram moles of methylbromide per kilogram of catholyte,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan methyl bromide and in which each alkyl group has 1-18 carbon atoms,said current-carrier being in a concentration sufiicient to provide acatholyte having a conductivity of at least 0.01 ohm* cm.- and (c) fromabout 1 to moles of water per mole of said current-carrier,

(d) the rest of the catholyte consisting essentially of at least onealkanonitrile in which the alkyl group has 1-5 carbon atoms; and

(C) continuously recirculating through the anode compartment a stream ofa liquid anolyte which initially consists essentially of a solution of(1) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monobromide which has a higher reduction potentialthan methyl bromide and in which each alkyl group has 1-18 carbon atoms,in a concentration sufficient to provide an anolyte having aconductivity of at least 0.01 ohm cmf (2) in an alkanonitrile in whichthe alkyl group has 1-5 carbon atoms; and

(D) continuously withdrawing a portion of the catholyte from therecirculating catholyte stream that has passed through the cathodecompartment and (D adding to the recirculating catholyte stream beforeit reenters the cathode compartment additional amounts of said methylbromide, currentcarrier, Water and alkanonitrile as may be necessary toreplace those consumed in the electrolysis and those withdrawn and toprovide a re circulating catholyte stream entering the cathodecompartment which has those ingredients in desired concentrations andrelative proportions within the ranges specified in (a) to (d),inelusive;

(E) simultaneously withdrawing a portion of the anolyte from therecirculating anolyte stream that has passed through the anodecompartment and (E adding to the recirculating anolyte stream before itreenters the anode compartment additional amounts of saidcurrent-carrier and alkanonitrile as may be necessary to replace thoseconsumed in the electrolysis and those withdrawn and to provide arecirculating anolyte stream entering the anode compartment which has aconductivity of at least 0.01 ohm" cmf and (F) recovering tetramethyllead from the withdrawn portion of the catholyte.

16. A continuous process for the electrolytic production of tetraalkyllead compounds at a lead cathode in an electrolytic cell having acathode of lead shot, an anode of a material which is resistant toattack by halogens of atomic numbers 17 to 53, and a current-permeablepartition made of member of the group consisting of parchment paper andan ion exchange resin separating the cell into a cathode compartment andan anode compartment, which process comprises (A) passing anelectrolyzing direct electric current through the cell at a voltagesufficient to provide and maintain a current density of from about 0.05to about 0.5 amp./ sq. cm. of efiective cathode area (B) whilecontinuously recirculating through the cathode compartment at atemperature of from about 20 C. to about 80 C. a stream of a liquidcatholyte which initially consists essentially of (a) from about 0.1 toabout 3 gram moles per kilogram of catholyte of an alkyl halide in whichthe alkyl group has 1-10 carbon atoms 30 and the halogen atom has anatomic number of at least 17,

(b) a current-carrier which consists of at least one current-carryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1-18 carbonatoms and the halogen atom has an atomic number of at least 17, saidcurrent-carrier being in a concentration suflicient to provide acatholyte having a conductivity of at least 0.001 ohmcmrand (c) fromabout 1 to 20 moles per mole of said current-carrier of at least onehydroxylic compound of the class consisting of water and alkanols of 1-4carbon atoms,

((1) the rest of the catholyte consisting essentially of an inertnonhydroxylic organic solvent for both said alkyl halide and saidcurrent-carrier which solvent has a reduction potential higher than saidalkyl halide and an oxidation potential higher than saidcurrent-carrier; and

(C) continuously recirculating through the anode compartment at atemperature of from about 20 C. to about C. a stream of a liquid anolytewhich initially consists essentially of a solution of (1) acurrent-carrier which consists of at least one currentcarryingtetraalkyl ammonium monohalide which has a higher reduction potentialthan said alkyl halide and in which each alkyl group has 1-18 carbonatoms and the halogen atom has an atomic number of at least 17 in aconcentration sutficient to provide an anolyte having a conductivity ofat least 0.001 ohmcm.

(2) in an inert solvent having a reduction potential at least as high assaid alkyl halide and an oxidation potential higher than saidcurrentcarrier; and

(D) continuously withdrawing a portion of the catholyte from therecirculating catholyte stream that has passed through the cathodecompartment and (D adding to the recirculating catholyte stream beforeit reenters the cathode compartment additional amounts of said alkylhalide, currentcarrier, hydroxylic compound and solvent as may benecessary to replace those consumed in the electrolysis and thosewithdrawn and to provide a recirculating catholyte stream entering thecathode compartment which has those ingredients in desiredconcentrations and relative proportions within the ranges specified in(a) to (d), inclusive;

(E) simultaneously withdrawing a portion of the anolyte from therecirculating anolyte stream that has passed through the anodecompartment and (E adding to the recirculating anolyte stream before itreenters the anode compartment additional amounts of saidcurrent-carrier and solvent as may be necessary to replace thoseconsumed in the electrolysis and those withdrawn and to provide arecirculating anolyte stream entering the anode compartment which has aconductivity of at least 0.001 ohm-V cm.

(F) adding lead shot to the cathode as may be necessary to replace thatconsumed by the electrolysis and to maintain the effective area of thecathode substantially constant; and

(G) recovering tetraalkyl lead from the withdrawn portion of thecatholyte.

17. A continuous process for the electrolytic production of tetramethyllead at a lead cathode in an electrolytic cell having a cathode of leadshot, an anode of a material 7 difierent from that of the cathode andwhich is resistant 31 to attack by halogens of atomic numbers 17 to 53,and a current-permeable partition of parchment paper separating the cellinto a cathode compartment and an anode compartment, which processcomprises (A) passing an electrolyzing direct electric current throughthe cell at a voltage sufiicient to provide and maintain a currentdensity of from about 0.05 to about 0.5 amp/sq. cm. of effective cathodearea (B) while continuously recirculating through the cathodecompartment at a temperature of from about 40 C. to about 50 C. a streamof a liquid catholyte which initially consists essentially of (a) fromabout 1 to about 2 gram moles of methyl bromide per kilogram ofcatholyte,

(b) from about 0.25 to about 0.5 gram mole of tetraethyl ammoniummonobromide per kilogram of catholyte,

(c) from about 3 to about 10 moles of water per mole of said tetraethylammonium monobromide,

(d) the rest of the catholyte consisting essentially of acetonitrile;and

(C) continuously recirculating through the anode compartment at atemperature of from about 40 C. to about 50 C. a stream of a liquidanolyte which initially consists essentially of a solution of (1)tetraethyl ammonium monobromide in a concentration of from about 5% toabout by weight (2) in water; and

(D) continuously withdrawing a portion of the catholyte from therecirculating catholyte stream that has passed through the cathodecompartment and (D adding to the recirculating catholyte stream beforeit reenters the cathode compartment additional amounts of said methylbromide, tetra ethyl ammonium monobromide, water and acetonitrile as maybe necessary to replace those consumed in the electrolysis and thosewithdrawn and to provide a recirculating catholyte 32 stream enteringthe cathode compartment which has those ingredients in desired relativeproportions within the ranges specified in (a) to (d), inclusive;

(E) simultaneously withdrawing a portion of the anolyte from therecirculating anolyte stream that has passed through the anodecompartment and (E adding to the recirculating anolyte stream before itreenters the anode compartment additional amounts of said tetraethylammonium monobromide and water as may be necessary to replace thoseconsumed in the electrolysis and those withdrawn and to provide arecirculating anolyte stream entering the anode compartment which hasthose ingredients in desired relative proportions within the rangesspecified in (1) and (2), and

(E withdrawing from the anode compartment water-immiscible tetraethylammonium polybromide as may be necessary to avoid its accumulation inthe anode compartment to an undesirable extent;

(F) adding lead shot to the cathode as may be necessary to replace thatconsumed by the electrolysis and to maintain the effective area of thecathode substantially constant; and

(G) recovering tetramethyl lead from the withdrawn portion of thecatholyte.

References Cited UNITED STATES PATENTS 1 ,539,297 5/ 1925 Calingaert20472 1,567,159 12/1925 Mead 20472 3,234,112 2/1966 Braithwaite 204593,254,009 5/1966 Ziegler et a1. 20459 JOHN H. MACK, Primary Examiner.

H. M. FLOURNOY, Assistant Examiner.

1. AN ELECTROLYTIC PROCESS FOR PRODUCING TETRALKYL LEAD COMPOUNDS AT ALEAD CATHODE IN AN ELECTROLYTIC CELL HAVING A LEAD CATHODE, AN ANODE OFA MATERIAL WHICH IS RESISTANT TO ATTACK BY HALOGENS OF ATOMIC NUMBERS 17TO 53, AND A CURRENT-PERMEABLE PARTITION SEPARATING THE CATHOLYTE FROMTHE ANOLYTE, WHICH PROCESS COMPRISES (A) PASSING AN ELECTROLYZING DIRECTELECTRIC CURRENT THROUGH (B) A LIQUID CATHOLYTE WHICH INITIALLY CONSISTSESSENTIALLY OF (A) AN ALKYL HALIDE IN WHICH THE ALKYL GROUP HAS 1-10CARBON ATOMS AND THE HALOGEN ATOM HAS AN ATOMIC NUMBER OF AT LEAST 17,(B) A CURRENT-CARRIER WHICH CONSISTS OF AT LEAST ONE CURRENT-CARRYINGTETRALKYL AMMONIUM MONOHALIDE WHICH HAS A HIGHER REDUCTION POTENTIALTHAN SAID ALKYL HALIDE AND IN WHICH EACH ALKYL GROUP HAS 1-18 CARBONATOMS AND THE HALOGEN ATOM HAS AN ATOMIC NUMBER OF AT LEAST 17, SAIDCURRENT-CARRIER BEING IN A CONCENTRATION SUFFICIENT TO PROVIDE ACATHOLYTE HAVING A CONDUCTIVITY OF AT LEAST 0.001 OHM-1 CM.-1, AND (C)FROM ABOUT 1 TO 20 MOLES PER MOLE OF SAID CURRENT-CARRIER OF AT LEASTONE HYDROXYLIC COMPOUND OF THE CLASS CONSISTING OF WATER AND ALKANOLS OF1-4 CARBON ATOMS; AND (C) A LIQUID ANOLYTE WHICH INITIALLY CONSISTSESSENTIALLY OF A SOLUTION OF (1) A CURRENT-CARRIER WHICH CONSISTS OF ATLEAST ONE CURRENT-CARRYING TETRAALKYL AMMONIUM MONOHALIDE WHICH HAS AHIGHER REDUCTION POTENTIAL THAN SAID ALKYL HALIDE AND IN WHICH EACHALKYL GROUPS HAS 1-18 CARBON ATOMS AND THE HLAOGEN ATOM HAS AN ATOMICNUMBER OF AT LEAST 17, IN A CONCENTRATION SUFFICIENT TO PROVIDE ANANOLYTE HAVING A CONDUCTIVITY OF AT LEAST 0.001 OHM-1CM.-1 0.001OHM-1CM.-U, (2) IN AN INERT SOLVENT HAVING A REDUCTION POTENTIAL ATLEAST AS HIGH AS SAID ALKYL HALIDE AND AN OXIDATION POTENTIAL HIGHERTHAN SAID CURRENTCARRIER; (D) DURING THE ELECTROLYSIS, ADJUSTING THEAMOUNTS OF THE CURRENT-CARRIER IN THE CATHOLYTE AND THE ANOLYTE AS MAYBE NECESSARY TO MAINTAIN THEIR CONDUCTIVITIES AT AT LEAST 0.001OHM-1CM9-1 AND ADJUSTING THE AMOUNT OF THE HYDROXYLIC COMPOUND IN THECATHOLYTE AS MAY BE NECESSARY TO MAINTAIN THE CONCENTRATION THEREOFWITHIN THE RANGE OF FROM ABOUT 1 TO ABOUT 20 MOLES PER MOLE OF SAIDCURRENT-CARRIER; AND (E) RECOVERING TETRAALKYL LEAD FROM THE CATHOLYTE.